Physical checks by customs would probably only be carried out based on tip-offs

No, the EU official said, there would be no systematic checks on the Irish Sea. Well, perhaps, in relation to live animals, she admitted. And they are already checked, she said.

Charged with explaining how the Northern Ireland backstop protocol would work in practice, she emphasised a new “decentralised” system based on a computer filing of customs declarations, barcode checking and supervision by regulatory authorities of goods either at factories where they are produced or when they arrived at destinations in Northern Ireland.

The backstop provisions of the withdrawal agreement are only supposed to kick in after the end of the UK’s transition period at the end of 2020. Or if the transition is extended by mutual agreement, which it can be – once – at the end of that extended period.

Then, if the EU and the UK have still failed to agree on the shape of a future relationship, the backstop will kick in. At that point the UK will downgrade its transition status as a member of both the customs union and the single market to one simply involving membership of a common customs area that will encompass the whole of the UK and Northern Ireland.

NI divergence

That will mean being part of an arrangement that involves no customs tariffs or quotas on its internal trade with the EU, and a continued commitment to the EU’s commercial policy (that is, with no right to strike its own trade deals internationally).

But border controls are about more than customs. They also ensure that importers conform to local regulations – including safety, labour standards and state aids. To safeguard the frictionless border in Ireland, Northern Ireland would be required by the withdrawal agreement then to implement stricter controls on goods coming in than the rest of the UK.

The purpose of negotiators, the EU official, said was to “minimise” such controls. They certainly do not constitute anything as dramatic as a customs border or pose a threat to the constitutional integrity of the UK, it is argued in Brussels.

On a boat from Liverpool to Belfast, or at either port, the official said, barcodes on goods in transit could be scanned. Physical checks at destination by customs officials would probably only be carried out on a “risk-based” assessment of tip-offs. Customs declarations could be filed online before trucks ever left.

The light-touch enforcement of regulatory alignment would be in sharp contrast to the necessity at Dublin Port or in Calais for full customs-like controls.

If, and only if, it proves necessary to invoke the insurance backstop.